Abbie Fentress Swanson reported for Harvest Public Media in Columbia, Mo., while based at KBIA.

Eleven miles northeast of Centralia, Mo., five U.S. Geological Survey scientists don waders and bright reflective life jackets to wade into Goodwater Creek. Plenty of fish live in the stream’s murky slow-moving waters, along with snakes, crayfish, mussels and snapping turtles. On this overcast morning, the team collects water samples and checks submerged cages of fathead minnows for eggs.

Goodwater Creek is one of a number of Missouri streams that this crew will visit this summer. After collecting samples, the scientists will test the water for hundreds of pesticides and nutrients used in farming. Similar teams of chemists, hydrologists, toxicologists and biologists are wading into other streams all across the Midwest – from Ohio to Nebraska – 100 streams in total. This is the first time scientists have tested for so many chemicals in a whole region’s waters or considered the impact of ag runoff on fish, frogs, bugs and algae at this scale.

The U.S. Geological Survey hopes to eventually use the findings from this study to make models that will calculate the concentrations of contaminants, nutrients and sediment in other Midwestern streams and predict how they will change the reproduction and development of fish, frogs, bugs and algae.

The study is costing the Geological Survey $6 million, including the time of about 60 scientists this summer. The group partnered with the Environmental Protection Agency to complete the assessment, which is contributing another $570,000.

“These aren’t the kinds of studies that are done routinely because they are pretty difficult to do,” said Papoulias. “But we know that some of these chemicals that we're finding in the runoff from the ag fields can affect (aquatic) reproduction and egg production. Whether they are at the concentrations that can do that or not we don’t know yet. That's what the chemists are going to be helping us with.”

Chemist Dave Alvarez quietly collects water at equal distances across Goodwater Creek by dipping his sampler, a plastic bottle attached to a long rod, deep into the stream. Although the lab results are a ways off, he says it would not surprise him to find atrazine in this stream, especially because the U.S. Department of Agriculture has found that runoff is 85 percent of the stream flow in this creek’s watershed.

The scientists chose summer as the season to complete the fieldwork because it’s when fish are spawning and farmers are applying the most pesticides and fertilizer to their fields.

“Atrazine is going to be is one of the ones they're going to be applying early in the season,” Alvarez said. “You want to try to get it soon after application, especially with all the storms we've been having. It's your greatest chance for runoff in the streams.”

Farmers widely use atrazine to kill weeds in fields of corn, sorghum and sugar cane. The chemical was found in about 90 percent of the over 1,000 samples the U.S. Geological Survey collected from streams in agricultural areas nationwide (PDF). U.S. Rep. Keith Ellison of Minnesota introduced legislation to ban the chemical in April, which environmental advocates argue has been linked to reproductive problems in fish, mammals and even humans.

In their comprehensive study of Midwestern streams, the scientists also want to find out the effect mercury has on fish and the levels of livestock hormones in the water. The big unknown, though, is the weed killer glyphosate – a chemical compound produced by Monsanto known by the trade name Roundup.

“Glyphosate's come in as the largest herbicide used now where 20 years ago its use was pretty small,” said hydrologist Peter Van Metre, one of the scientists in charge of the study.

The high cost of lab work for glyphosate is one of the reasons it hasn’t been tested for much in streams, Van Metre says.

“Glyphosate is a very difficult compound,” he said. “It costs a third to half as much for just a glyphosate analysis as it does for all these other pesticides.”

After wading 150 yards downstream, the biologists successfully hauled up six cages of minnows from the creek bottom. The minnows were alive but there were no fish eggs, probably because recent wet weather in central Missouri brought the water temperature down to 16.9 degrees Celsius, too cool for spawning.

Although the scientists got mixed results on this trip, they’ll be at Goodwater Creek every other day until the end of July to collect water and check for fish eggs. The crew will also visit other streams they’re responsible for at least once a week. Results will trickle in after the fieldwork’s complete in August, and Van Metre’s looking forward to getting some answers.

“We know in the big picture that land use – intensive land use – harms water quality. When you have real intensive agriculture, urban development, the water quality goes downhill. But it's not uniform, it varies…” Van Metre said. ”It's really trying to understand all the different factors that affect the health of the streams. And then by doing that get a better idea of what we need to do to be able to farm but have healthier streams.”

What's in your stream water?

Midwest waterways are getting lots of attention this summer. Scientists from the U.S. Geological Survey and the Environmental Protection Agency have immersed themselves in the ecology of 100 streams from Ohio to Nebraska. It’s a first-of-its kind effort to understand how ag runoff is not just changing the water but affecting the critters that live there. Click on the map below to see which Corn Belt streams the scientists will be wading into.